1. Field of the Invention
The invention relates to a fuel cell system for generating an electricity using a hydrogen gas and a method for operating the same.
2. Description of the Related Art
In recent years, under consideration of the environment, a vehicle has been developed which uses electricity generated by a fuel cell as a power source. The fuel cell system loaded in such a vehicle is preferably compact in size, light in weight and high in the efficiency of using energy. An example of the related art viewed from this standpoint is disclosed in JP-A-2000-67898.
The fuel cell system described in JP-A-2000-67898 is to cause a hydrogen occluding alloy in a hydrogen storing means to occlude the hydrogen not consumed by and exhausted from a fuel cell or a reformed hydrogen gas from a reforming device.
However, the hydrogen storing means provides a time lag from the electrochemical reaction in the fuel cell to the extraction of a current. Such a fuel cell system cannot swiftly increase supplied electricity according to an increase in a required output, and hence could not give sufficient transition response.
The fuel cell system with insufficient transition response requires a long time taken from when a driver operates an accelerator to when the vehicle is actually accelerated or decelerated. If the quantity to be treated by a reforming device is excessively increased or decreased in order to improve the transition response, the burden is given to the fuel cell system.
It is an object of the invention to optimize the generating efficiency of the fuel cell system so that a hydrogen gas and energy are efficiently used to enhance the response to an output change.
In order to solve the problem described above, the invention is a fuel cell system including a fuel cell capable of supplying an electricity generated by an electrochemical reaction of a hydrogen gas and an oxygen gas to a load and a reforming device for creating the hydrogen gas to be supplied to the fuel cell by a reforming reaction, comprising:
an electric buffer for charging an electricity supplied by the fuel cell; and
a hydrogen buffer for accommodating the hydrogen gas supplied by the reforming device; characterized in that the quantity of the hydrogen gas corresponding to the generated electricity in the fuel cell is served by the quantity of the hydrogen gas discharged by the reforming device and the hydrogen buffer, and the electricity required by the load is served by the generated electricity of the fuel cell and the electricity discharged from the electric buffer.
In this fuel cell system, where the necessary electricity cannot be supplied with the aid of only the hydrogen gas supplied from the reforming device (e.g. reformer) during the transient period while the output changes, until the hydrogen gas supplied from the reforming device increases, the hydrogen gas previously accommodated in the hydrogen buffer is supplied to the fuel cell, and/or the electric energy previously stored in the electric buffer is supplied to the load, thereby serving the necessary electricity. On the other hand, the electricity generated owing to the hydrogen gas from the reforming device is surplus, the surplus electricity is filled in the electric buffer and the surplus hydrogen gas is accommodated. Such preparation for a next output change permits the energy to be employed effectively.
The invention is a fuel cell system, characterized in that when the necessary electricity consumed by the load increases, discharging of the electricity from the electric buffer is done preferentially to that of the hydrogen gas from the hydrogen buffer.
In this fuel cell system, since the electric buffer having the highest response to an increase in the necessary electricity is preferentially employed, the transition response of the fuel cell equipped electric vehicle can be improved.
The invention is a fuel cell system, characterized in that the hydrogen gas is discharged from the hydrogen buffer according to the remaining quantity of the electric energy stored in the electric buffer.
In this fuel cell system, since the hydrogen gas supplied from the hydrogen buffer with low response but high energy density is increased according to the remaining quantity of the electric buffer with a low energy density, the electricity can be supplied stably to serve the necessary electricity for the load.
Further, the invention is a fuel cell system, characterized in that the hydrogen gas is discharged from the reforming device according to the remaining quantity of the hydrogen gas accommodated in the hydrogen buffer.
In this fuel cell geminating system, where the necessary electricity cannot be served by the electricity generated by the fuel cell with the aid of the hydrogen buffer, the hydrogen gas supplied from the reforming device with the lowest response but high stability is increased, thereby continuing to supply the necessary electricity surely.
In accordance with this invention, there is provided a method of operating a fuel cell system wherein the electricity generated by a fuel cell by an electrochemical reaction of a hydrogen gas obtained from a reforming reaction in are forming device and an oxygen gas is supplied to a load; a necessary electricity consumed by the load and the electricity corresponding to excess/shortage of the electricity supplied from the fuel cell are charged in or discharge from an electric buffer; and the hydrogen gas corresponding to the excess/shortage in the quantity of the necessary hydrogen gas for the fuel cell and the quantity of the hydrogen gas supplied from the reforming device is charged in or discharged from a hydrogen buffer accommodating a hydrogen occluding alloy, characterized in that when the necessary electricity increases, after the electricity supplied from the electric buffer to the load has been increased, the quantity of the hydrogen gas supplied from the hydrogen buffer to the fuel cell is increased and the electricity generated by the fuel cell is increased, thereby serving the necessary electricity.
In this method of operating a fuel cell system, when the necessary electricity is increased, at an initial time, the electricity is supplied to the load from the electric buffer with the highest response to enhance the transition response. Next, the generated electricity is increased with the aid of the hydrogen gas supplied from the hydrogen buffer with the high energy density so that the electricity supply can be can be done stably.
The is a method of operating a fuel cell system, wherein after the quantity of the hydrogen gas supplied from the hydrogen buffer has been increased, the quantity of the hydrogen gas supplied from the reforming device so that the electricity generated by the fuel cell is increased to serve the necessary electricity.
In the method of operating of a fuel cell system, after the response of electricity supply in the transient time while the necessary electricity increases has been enhanced with the aid of the electric buffer and hydrogen buffer, the hydrogen gas supplied from the reforming device is increased so that the electricity supply can be done stably.